Powder metal polymer composites

ABSTRACT

A composite part including: a compacted powder composition; and a polymer composite comprising nanometer-sized and/or micrometer-sized reinforcement structures, wherein the composite part has an interpenetrating network between the compacted powder composition and the polymer composite and wherein the reinforcement structures comprise one or more of: particles, platelets, fibers, whiskers, and tubes. A composite part formed by a method including compacting a powder composition including a lubricant into a compacted body; heating the compacted body to a temperature above the vaporization temperature of the lubricant such that the lubricant is substantially removed from the compacted body; subjecting the obtained heat treated compacted body to a liquid polymer composite including nanometer-sized and/or micrometer-sized reinforcement structures; and solidifying the heat treated compacted body comprising liquid polymer composite by drying and/or by at least one curing treatment.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.12/529,046, filed on Sep. 29, 2009, which is a National Stageapplication continuation of International Application No.PCT/SE2008/050261, filed on Mar. 7, 2008, which claims the benefit ofU.S. Provisional Application No. 60/907,115, filed on Mar. 21, 2007, andwhich claims the benefit of Danish Application No. PA200700435, filed onMar. 21, 2007. The entire contents of each of U.S. application Ser. No.12/529,046, International Application No. PCT/SE2008/050261, U.S.Provisional Application No. 60/907,115, and Danish Application No.PA200700435 are hereby incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates to a new method of producing a compositepart. The method comprises the step of compaction of a powdercomposition into a compacted body, followed by a heat treatment stepwhereby an open pore system is created and followed by an infiltrationstep. The invention further relates to a composite part.

BACKGROUND

Soft magnetic materials can be used for applications such as corematerials in inductors, stators, and rotors for electrical machines,actuators, sensors, and transformer cores. Traditionally, soft magneticcores, such as rotors and stators in electric machines, are made ofstacked steel-sheet laminates. However, in the last few years there hasbeen a keen interest in so called Soft Magnetic Composite (SMC)materials. The SMC materials are based on soft magnetic particles,usually iron based, with an electrically insulating coating on eachparticle. By compacting the insulated particles, optionally togetherwith lubricants and/or binders, using the traditionally powdermetallurgy process, the SMC parts are obtained. By using the powdermetallurgical technique it is possible to produce materials having ahigher degree of freedom in the design of the SMC part compared to usingsteel-sheet laminates, as the SMC material can carry a three dimensionalmagnetic flux and as three dimensional shapes can be obtained with thecompaction process.

As a consequence of the increased interest in the SMC materials,improvements of the soft magnetic characteristics of the SMC materialsis the subject of intense studies in order to expand the utilization ofthese materials.

In order to achieve such improvement, new powders and processes arecontinuously being developed.

Two key characteristics of an iron core component are its magneticpermeability and core loss characteristics. The magnetic permeability ofa material is an indication of its ability to become magnetized or itsability to carry a magnetic flux. Permeability is defined as the ratioof the induced magnetic flux to the magnetizing force or fieldintensity. When a magnetic material is exposed to an alternating field,such as for example an alternating electric field, energy losses occurdue to both hysteresis losses and eddy current losses. The hysteresisloss is brought about by the necessary expenditure of energy to overcomeretained magnetic forces within the iron core component and isproportional to the frequency of e.g. the alternating electrical field.The eddy current loss is brought about by the production of electriccurrents in the iron core component due to the changing flux caused byalternating current (AC) conditions and is proportional to the square ofthe frequency of the alternating electrical field. A high electricalresistivity is then desirable in order to minimize the eddy currents andis of special importance at higher frequencies, such as for exampleabove about 60 Hz. In order to decrease the hysteresis losses and toincrease the magnetic permeability of a core component it is generallydesired to heat-treat a compacted part whereby the induced stresses fromthe compaction are reduced. Furthermore, in order to reach desiredmagnetic properties, such as high magnetic permeability, high inductionand low core losses, high density of the compacted part is often needed.High density is here defined as a density above 7.0, preferably above7.3 most preferably about 7.5 g/cm³ for an iron-based compacted part.

In addition to the soft magnetic properties, sufficient mechanicalproperties are essential. High mechanical strength is often aprerequisite to avoid introducing cracks, laminating, and break-outs andto achieve good magnetic properties of compacts which after compactionand heat treatment have been subjected to machining operations. Also,lubricating properties of an impregnated polymer network can increasethe lifetime of cutting tools considerably.

In order to be able to expand the utilization of SMC components, highstrength at elevated temperature is an important property such as forexample for components used in applications such as motor cores,ignition coils, and injection valves in automobiles.

By admixing a binder to the SMC powder before compaction, improvedmechanical strength of the compacted and heat treated component can beobtained. In the patent literature several kinds of organic resins, suchas thermoplastics and thermoset resins, inorganic binders such assilicates or silicon resins, are reported. The heat treatment of organicresin bonded components is restricted to comparatively low temperatures,below about 250° C., as the organic material destroys at temperatureabove about 250° C. The mechanical strength of heat treated organicbonded components at ambient conditions is good, but deteriorates above100° C. Inorganic resins can be subjected to higher temperatures withouteffecting the mechanical properties, however, the use of inorganicbinders are often associated with poor powder properties, poorcompressibility, poor machinability and often needed in high amountsthat precludes higher density levels.

U.S. Pat. No. 6,485,579 describes a method of increasing the mechanicalstrength of SMC component by heat treating the component in the presenceof water vapor. Higher values for the mechanical strength are reportedcompared to components heat treated in air, however, increased corelosses are obtained. A similar method is described in WO 2006/135324where high mechanical strength in combination with improved magneticpermeability are obtained provided metal free lubricants are used. Thelubricants are evaporated in a non-reducing atmosphere before subjectingthe component to water vapor. However, the oxidation of the ironparticles, when the component is subjected to steam treatment, will alsoincrease the coercive forces and thus core losses.

Impregnation, infiltration, and sealing of die casts or powder metal(P/M)-components, e.g., by an organic network, are known methods inorder to prevent surface corrosion or seal surface porosity. Highlydependent on density and processing conditions of P/M parts, the degreeof penetration of the organic network will vary. Low density levels(<89% of the theoretical density) and mild sintering conditions or heattreatments provide for easy penetration and full impregnation. For highperformance materials having high density and low porosity theprerequisites to reach full impregnation are limited.

Impregnation of SMC components to improve the machinability forproducing prototype components, or to improve the corrosion resistance,is shown for example in patent application JP 2004/178,643 where theimpregnation liquid constitutes of oils in general. Besides themarginally improved machinability of this method it results in greasyand slippery surfaces, worse to handle. Oil does not greatly improvecutting tool life because it never becomes solid. In the same way,uncured or soft sealants offer little value to machining. A reliablecure mechanism for the polymer together with high mechanical strength ofthe composite part is the best assurance of consistent machiningperformance.

U.S. Pat. No. 6,331,270 and U.S. Pat. No. 6,548,012 both describeprocesses for manufacturing AC soft magnetic components from non-coatedferromagnetic powders by compaction of the powders together with asuitable lubricant followed by heat treatment. It is also stated thatfor applications requiring higher mechanical strength, the componentsmay be impregnated, for example with epoxy resin. As non-coated powdersare used, these methods are less suitable due to high eddy currentlosses obtained if the components are used for applications subjected tohigher frequencies, above about 60 Hz. U.S. Pat. No. 5,993,729 dealsmainly with uncoated iron-based powder and infiltration of low densitycompacts produced with the aid of die wall lubrication. The patent alsomentions powders, wherein the particles are individually coated with anon-binding electro-insulating layer, comprising of oxides appliedeither by sol-gel process or by phosphatation. The compacted softmagnetic elements according to U.S. Pat. No. 5,993,729, are restrictedto applications working at low frequencies, below about 60 Hz, due topoor electrical resistivity. In addition, the oxidative heat treatmentof powder or compacts before the impregnation process will restrict orfully prevent pore penetration of the impregnating liquid, especiallyfor compacts of high density, above about 7.0 g/cm³, and especiallyabove about 7.3 g/cm³.

OBJECT OF THE INVENTION

An object of the present invention is to provide a method for increasingthe mechanical strength of heat treated (SMC) components, especiallycomponents having a density above about 89% of the theoretical density,(for components produced from iron-based powders above about 7.0 g/cm³.)and having lower coersivity compared to SMC compacts where highermechanical strength has been achieved by conventional heat treatment inan oxidizing atmosphere.

A further object of the invention is to provide a method formanufacturing impregnated components having both high density and highmechanical strength at elevated temperatures, for example above about150° C.

SUMMARY OF THE INVENTION

The above mentioned objects of the invention are obtained by a methodfor producing composite parts, the method comprising the steps ofcompacting a powder composition comprising a lubricant into a compactedbody; heating the compacted body to a temperature above the vaporizationtemperature of the lubricant such that the lubricant substantially isremoved from the compacted body, subjecting the obtained heat treatedcompacted body to a liquid polymer composite comprising nanometer-sizedand/or micrometer-sized reinforcement structures, and solidifying theheat treated compacted body comprising liquid polymer composite bydrying and/or by at least one curing treatment.

By subjecting the heat treated compacted body to a liquid polymercomprising nanometer-sized and/or micrometer-sized reinforcementstructures, the liquid polymer composite is enabled to impregnate and/orinfiltrate the heat treated compacted body, also if the compacted bodycomprises small cavities. By subsequently solidifying the heat treatedcompacted body comprising the liquid polymer composite provides aninterpenetrating network comprising nanometer-sized and/ormicrometer-sized reinforcement structures which thereby results in aheat treated compacted body with increased mechanical strength andincreased machinability compared to conventional impregnation and/orinfiltration methods.

The organic interpenetrating network of the present invention, givesbesides an improved mechanical strength, also enhanced machinabilityproperties, as compared to conventional impregnation or infiltrationmethods. The organic polymer may be chosen to give the impregnatedcompact high mechanical strength at elevated temperatures, above about100 MPa at about 150° C.

The present invention allows successful impregnation of compacts of upto 98% of theoretical density. Also, the introduction of aninterpenetrating network, which may have lubricating properties, into acompacted body may considerably increase the life time of cutting toolsand machinery used to process the heat treated compacted body comparedto conventional impregnation and/or infiltration methods.

In an embodiment of the invention, the powder composition furthercomprises a soft magnetic powder, preferably iron-based soft magneticparticles, wherein the particles further comprise an electricallyinsulated coating.

Thus, the method may also produce soft magnetic parts/components andthereby combine the increased mechanical strength of the heat treatedcompacted body with improved soft magnetic properties.

Still further, the method may improve the machinability properties of anSMC component, which may preserve good magnetic properties after amachining operation.

Additionally, the method enables manufacturing of impregnated softmagnetic components having both high density and high mechanicalstrength. The increased density and mechanical strength may also bepresent at elevated temperatures, for example above about 150° C.

Additionally, the invention thus provides a method for producing a softmagnetic composite component having noise reducing or acoustic dampingproperties for, e.g. noise caused by dynamic forces such asmagnetostriction forces.

In an embodiment of the invention, the reinforcement structures comprisecarbon nanotubes preferably single-wall nanotubes.

The carbon nanotubes provide increased strength to the heat treatedcompacted body. The reinforcement structures may have been chemicallyfunctionalized

In an embodiment of the invention, the method further comprises the stepof sintering the heat treated body after the heat treatment of thecompacted body.

In this way, the method according to the invention may be applied on forexample sintered parts. Thus, components subjected to heatingtemperatures at which sintering occur may also be produced by themethod. In case of sintering, the powder particles do not need to becoated.

Further embodiments of the method are described in the detaileddescription below together with the dependent claims and the figures.

Additionally, the invention further describes a composite part.

DETAILED DESCRIPTION OF THE INVENTION

In contrast to known impregnation or infiltration methods, the presentinvention enables the polymer composite liquid to fully penetrate bodieseven of such high densities as 7.70 g/cm³ for compacts produced of ironbased powders. An impregnated SMC compact according to the presentinvention can thus exhibit unexpectedly high mechanical strength in awide interval from cryogenic to high temperatures (for example aboveabout 150° C.), improved machining properties, and improved corrosionresistance.

A further aspect of polymer impregnated SMC compacts is an apparentdamping of acoustic properties (i.e. noise reduction) at high inductionand high frequency applications. The noise arising from dynamic forcesas e.g. magnetostriction, or other mechanical loads, can be reduced withan impregnation, as compared to non-impregnated compacts. The noisereduction increases with the volume fraction of impregnant (i.e. lowercompacted density).

The soft magnetic powders used according to the present invention may beelectrically insulated iron-based powders such as pure iron powders orpowders comprising an alloy of iron and other elements such as Ni, Co,Si, or Al. For example, the soft magnetic powder may consistsubstantially of pure iron or may at least be iron-based. For example,such a powder could be e.g. commercially available water-atomized orgas-atomized iron powders or reduced iron powders, such as sponge ironpowders.

The electrically insulating layers, which may be used according to theinvention, may be thin phosphorous comprising layers and/or barriersand/or coatings of the type described in the U.S. Pat. No. 6,348,265,which is hereby incorporated by reference. Other types of insulatinglayers may also be used and are disclosed in e.g. the U.S. Pat. Nos.6,562,458 and 6,419,877. Powders, which have insulated particles andwhich may be used as starting materials according to the presentinvention, are e.g. Somaloy®500 and Somaloy®700 available from HöganäsAB, Sweden.

The type of lubricant used in the metal powder composition may beimportant and may, for example, be selected from organic lubricatingsubstances that vaporize at temperatures above about 200° C. and ifapplicable below a decomposition temperature of the electricallyinsulating coating or layer

The lubricant may be selected to vaporize without leaving any residuesthat can block pores and thereby prevent subsequent impregnation to takeplace. Metal soaps, for example, which are commonly used for diecompaction of iron or iron-based powders, leave metal oxide residues inthe component. However, in case of density less than 7.5 g/cm³, thenegative influence of these residues is less pronounced, permitting theuse of metal-containing lubricants at this condition.

Another example of lubricating agents are fatty alcohols, fatty acids,derivatives of fatty acids, and waxes. Examples of fatty alcohols arestearyl alcohol, behenyl alcohol, and combinations thereof. Primary andsecondary amides of saturated or unsaturated fatty acids may also beused e.g. stearamide, erucyl stearamide, and combinations thereof. Thewaxes may, for example, be chosen from polyalkylene waxes, such asethylene bis-stearamide.

The amount of lubricant used may vary and may for example be 0.05-1.5%,alternatively 0.05-1.0%, alternatively 0.1-0.6% by weight of thecomposition to be compacted.

An amount of lubricant of less than 0.05% by weight of the compositionmay give poor lubricating performance, which may result in scratchedsurfaces of the ejected component, which in turn may block the surfacepores and complicate the subsequent vaporization and impregnationprocesses. The electrical resistivity of compacted components producedfrom coated powders may be affected negatively, mainly due to adeteriorated insulating layer, caused by both poor internal and externallubrication.

An amount of lubricant of more than 1.5% by weight of the compositionmay improve the ejection properties but generally results in too lowgreen density of the compacted component, thus, giving low magneticinduction and magnetic permeability.

The compaction may be performed at ambient or elevated temperature. Thepowder and/or the die may be preheated before compaction. For example,the die temperature may be adjusted to a temperature of not more than60° C. below the melting temperature of the used lubricating substance.For example, for stearamide, the die temperature may be 40-100° C., asstearamide melts at approximately 100° C.

The compaction may be performed between 400 and 1400 MPa. Alternatively,the compaction may be performed at a pressure between 600 and 1200 MPa.

The compacted body may subsequently be subjected to heat treatment inorder to remove the lubricant in a non-oxidative atmosphere at atemperature above the vaporization temperature of the lubricant. In casethe powder is coated with an insulating layer—the heat treatmenttemperature may be below the temperature of the decompositiontemperature of the inorganic electrically insulating layer.

For example, for many lubricants and insulating layers this means thatthe vaporization temperature should be below 650° C., e.g. below 500° C.such as between 200 and 450° C. The method according to the presentinvention, however, is not particularly restricted to thesetemperatures. The heat treatment may be conducted in an inertatmosphere, in particular a non-oxidizing atmosphere, such as forexample nitrogen or argon.

If the heat treatment is conducted in an oxidative atmosphere, surfaceoxidation of the iron or iron-based particles may take place and mayrestrict or prevent an impregnant, (i.e. impregnation liquid) to flowinto the porous network of the compacted body. The extent of theoxidation is dependent on the temperature and oxygen potential of theatmosphere. For example, if the temperature is less than about 400° C.in air, an adequate penetration of impregnant can take place. This maygive the impregnated compact an acceptable mechanical strength, but mayyield an unacceptable stress relaxation with poor magnetic properties asa consequence.

The delubricated body may subsequently be immersed into an impregnant,for example in a impregnation container. Subsequently, the pressure inthe impregnation container may be reduced. After the pressure of theimpregnation container has reached approximately below 0.1 mbar, thepressure is returned to atmospheric, whereby the impregnant is forced toflow into the pores of the compacted body until the pressure isequalized. Depending on the viscosity of the impregnant, density of thecompact, and size of the compact, the time and pressure required tofully impregnate the compact may vary.

The impregnation may be conducted at elevated temperatures (for exampleup to 50° C.) in order to decrease the viscosity of the liquid andimprove the penetration of the impregnant into the compacted body, aswell as to reduce the time required for the process.

Further, the compact may be subjected to a reduced pressure and/orelevated temperatures before it is immersed in the impregnant. Thereby,entrapped air and/or condensed gases present inside the compacts may beremoved and thus, the subsequent impregnation may proceed faster. Thepenetration may also proceed faster and/or more completely if thepressure is raised above ambient pressure level after the impregnationtreatment in low pressure.

However, care must be taken that the stoichiometry of the impregnant isnot altered by losses of volite material during the vacuum process.Thus, the impregnation time, pressure, and temperature may be decided bya person skilled in the art in view of the component density, thetemperature and/or atmosphere wherein the component was heat treated, aswell as desired strength, penetration depth, and the type of impregnant.

The impregnation process is initiated at the surface of the compactedbody and penetrates in towards the center of the body. In some cases apartial impregnation may be accomplished and thus according to oneembodiment of the invention the impregnation process is terminatedbefore the surfaces of all particles of the compacted body have beensubjected to the impregnation liquid. In this case an impregnated crustmay surround an unimpregnated core. Thus, provided the degree ofpenetration has given the component an acceptable level of mechanicalstrength and machining properties, the impregnation process may beterminated before complete penetration throughout the compacted body hastaken place.

In cases where the chemical compatibility between the metal network ofthe compacted body and the impregnant is not favorable, the surface ofthe interpenetration voids of the compacted body may be treated withsurface modifiers, cross-linkers, coupling and/or wettability agents,such as organic functional silanes or silazanes, titanates, aluminates,or zirconates, prior to impregnation treatment according to theinvention. Other metal alkoxides as well as inorganic silanes,silazanes, siloxanes, and silicic acid esters may also be used.

In some cases where the penetration of the liquid polymer composite intothe compacted body is especially difficult, the impregnation process maybe improved with the help of magnetostriction forces. The parts, thecompacted body and the impregnation fluid, may thereby be exposed to anexternal alternating magnetic field during the impregnating process.

Superfluous impregnant may be removed before the impregnated compact iscured at elevated temperature and/or anaerobic atmosphere. Thesuperfluous impregnant may for example be removed by centrifugal forceand/or pressurized air and/or by an immersion in a suitable solvent.Procedures of impregnation, such as for example the methods employed bySoundSeal AB, Sweden, and P. A. System srl, Italy, may be applied. Theprocess of removing superfluous impregnant may, for example, beperformed batchwise in vacuum chambers and/or vacuum furnaces that arecommercially available.

The polymer systems for impregnation according to the present inventionmay, for example, be curable organic resins, thermoset resins, and/ormeltable polymers that solidify below their melting temperature to athermoplastic material.

The polymer system may be any system or combination of systems thatsuitably allow for integration with nanometer-sized structures byphysical and/or chemical forces such as for example Van der Waalsforces, hydrogen bonds, and covalent bonds.

In order to simplify handling and to use the resin in continuousoperations, the polymer systems may for example be chosen from the groupof resins which cure at elevated temperatures (e.g. above about 40° C.)and/or in an anaerobic environment. Examples of such polymer systems forimpregnation may, for example, be epoxy or acrylic type resins showinglow viscosity at room temperature and having good thermo stability.

Thermoset resins according to the present invention, may, for example,be cross-linked polymer species such as polyacrylates, cyanate esters,polyimides and epoxies. Thermoset resins exemplified by epoxies may beresins wherein cross-linking occurs between the epoxy resin speciescomprising epoxide groups and curing agents composing correspondingfunctional groups for crosslinking. The process crosslinking is termed“curing”.

The polymer system can be any system or combination of systems thatsuitably allow for integration with nanometer-sized structures byphysical and chemical forces as Van der Waals forces, hydrogen bonds,and covalent bonds.

Examples of epoxies include, but are not limited to, diglycidyl ether ofbisfenol A (DGBA), bisfenol F type, tetraglycidyl methylene dianiline(TGDDM), novolac epoxy, cycloaliphatic epoxy, brominated epoxy.

Examples of corresponding curing agents comprise, but are not limitedto, amines, acid anhydrides, and amides etc. The variety of curingagents may further be exemplified by amines; cycloalifatic amines suchas bis-paraminocyclohexyl methane (PACM), alophatic amines such astri-etylene-tetra-amine (TETA) and di-etylene-th-amine (DETA), aromaticamines such as diethyl-toluene-diamine and others.

Anaerobe resins may be selected from any polymer or oligomer base thatis crosslinked on removal of oxygen, exemplified by acrylics as urethaneacrylate, metacrylate, methyl methacrylate, methacrylate ester,polygycole di- or monoacrylate, allyl methacrylate, tetrahydro furfurylmethacrylate and more complex molecules ashydroxiethylmethacrylate-N—N-dimethyl-p-touidin-N-oxide and combinationshereof.

Thermoplastics according to the invention may be meltable materials thatalso may be heated for impregnation. Examples of materials forimpregnation comprise a range from low temperature polymers such aspolyethylene (PE), polypropylene (PP), ethylenevinyleacetate to hightemperature materials such as polyeterimide (PEI), polyimide (PI),fluorethylenepropylene (FEP), and polyphenylenesulfide (PPS),polyetersulfone (PES) etc. The polymer systems may further compriseadditives such as, but not limited to, plasticizers, anti-degradationagents as antioxidants, diluents, toughening agents, synthetic rubberand combinations thereof.

The polymer system design makes it possible to reach the desiredproperties of the impregnated compacted body such as improved mechanicalstrength, temperature resistance, acoustic properties and/ormachinability.

The present invention permits design and engineering of a variety ofpolymer phases for a variety of applications by incorporation ofnanometer-sized and/or micrometer-sized reinforcement structures such asfor example particles, platelets, whiskers, fibers, and/or tubes asfunctional fillers in the polymer systems. The term “nanometer-size” ishere meant as sizes wherein at least two dimensions of athree-dimensional structure is in the range of 1 nm to 200 nm. Also,micrometer-sized materials such as fibers, whiskers, and particles inthe range of 200 nm to 5 μm may, for example, be used when theinterpenetrating network voids in e.g. a compacted body are large.

These structures may contribute with improved properties to theinterpenetrating networks of the polymer systems/impregnants. Toaccomplish a desired dispergation in the polymer phase, thenanometer-size structures may be chemical functionalized. Thefunctionalized nanometer-size and/or micrometer-sized structures mayfurther be dispersed in the polymer phase by adding with compatiblesolvents, treating with heat, treating with vacuum, stirring,calendering, or ultrasonic treatment, forming a here denoted liquidpolymer composite.

Carbon nanotubes (CNT), i.e. single- or multi-walled nanotubes (SWNT,MWNT) and/or other nanometer-sized materials may, for example, be usedas reinforcement structures in the polymer systems.

At least two dimensions of each individual constituent of a functionalfiller and/or reinforcement structure may, for example, be less than 200nm, alternatively for example less 50 nm, and alternatively less than 10nm.

The shape of the functional filler and/or reinforcement constituentsmay, for example, be elongated, such as tubes and/or fibers and/orwhiskers for example showing lengths between 0.2 μm to 1 mm.

The surface of the functional filler and/or reinforcement constituentsmay, for example, be chemically functionalized in order to be compatiblewith a chosen polymer system. Thereby, the functional filler and/orreinforcement constituents may become substantially completely dispersedin the polymer system and to avoid aggregation. Such functionalizationmay, for example, be conducted using surface modifiers, cross-linkers,coupling- and/or wettability agents, which can be various types oforganic functional silanes or silazanes, titanates, aluminates, orzirconates. Other metal alkoxides as well as inorganic silanes,silazanes, siloxanes, and silicic acid esters may also be used.

Nanometer-sized structures, such as carbon nanotubes and nanoparticles,are available from many and increasing amount of suppliers. Polymerresins reinforced with CNT's are commercially available from for exampleAmroy Europe, Inc (Hybtonite®) or Arkema/Zyvex Ltd (NanoSolve®).

In general, any of the technical features and/or embodiments describedabove and/or below may be combined into one embodiment. Alternatively oradditionally any of the technical features and/or embodiments describedabove and/or below may be in separate embodiments. Alternatively oradditionally any of the technical features and/or embodiments describedabove and/or below may be combined with any number of other technicalfeatures and/or embodiments described above and/or below to yield anynumber of embodiments.

Although some embodiments have been described and shown in detail, theinvention is not restricted to them, but may also be embodied in otherways within the scope of the subject matter defined in the followingclaims. In particular, it is to be understood that other embodiments maybe utilized and structural and functional modifications may be madewithout departing from the scope of the present invention.

In device claims enumerating several means, several of these means canbe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims ordescribed in different embodiments does not indicate that a combinationof these measures cannot be used to advantage.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other features, integers, steps,components or groups thereof.

As can be seen from the following examples, a novel type of softmagnetic composite components can be obtained by the method according tothe invention.

EXAMPLES

The invention is further illustrated by the following non-limitingexamples.

Example 1

As starting material Somaloy® 700 available from Höganäs AB was used.One composition, (sample A), was mixed with 0.3 weight % of an organiclubricant, stearamide, and a second composition, (sample B), with 0.6 wt% of an organic lubricant binder, the polyamide Orgasol® 3501.

The compositions were compacted at 800 MPa into toroid samples having aninner diameter of 45 mm, outer diameter of 55 mm and height of 5 mm, andinto Transverse Rupture Strength samples (TRS-samples) to the densitiesspecified in table 1. The die temperature was controlled to atemperature of 80° C.

After compaction the samples were ejected from the die and subjected toheat treatment. Three compacts of sample A were treated at 530° C. for15 minutes in an atmosphere of air (A1) and nitrogen (A2, A3),respectively. Sample A2 was further subjected to impregnation accordingto the invention using an epoxy resin reinforced with CNT's. The thirdcompact of sample A, treated in nitrogen, was further subjected to steamtreatment at 520° C. according to the process described in WO2006/135324 (A3). A compact of sample B was treated at 225° C. for 60minutes in air.

Transverse Rupture Strength was measured on the TRS- samples accordingto ISO 3995. The magnetic properties were measured on toroid sampleswith 100 drive and 100 sense turns using a hystehsisgraph fromBrockhaus. The coercivity is measured at 10 kA/m, and the core loss ismeasured at 1T and 400 Hz.

TABLE 1 Coercive Heat Density TRS TS Force, Sample Additive TreatmentAtmosphere [g/cm3] [MPa] [MPa] H_(c) [A/m] A1 (ref) 0.30 wt % 530° C.,N2 7.54 43 8 200 A2 Stearamide 15 min N2 + Impreg. 7.54 120 62 180 A3N2 + Steam 7.54 130 66 220 B 0.60 wt % 225° C., AIR 7.40 105 40 300Polyamide 60 min

As can be seen from table 1, high mechanical strength of the samples canbe reached by a process according to the invention (A2), by internaloxidation (A3), or by adding an organic binder to the powder composition(B). However, the use of the organic binder restricts the heat treatmenttemperature to 225° C., giving poor magnetic properties. The steamtreated sample (A3), shows high strength, but high coercivity (H_(c))compared to the impregnated sample (A2). The sample produced accordingto the invention (A2) exhibit high mechanical strength in combinationwith low coercive force.

Example 2

An electrically insulated soft magnetic powder, Somaloy® 700, availablefrom Höganäs AB, was mixed with 0.5 wt % of stearamide (C), Ethylenebisstearamide wax (EBS wax) (D), and Zn-stearate (E), respectively, andcompacted to 7.35 g/cm³. The samples were further subjected to a heattreatment for 45 minutes in air at 350° C., or in an atmosphere ofnitrogen at 530° C. One sample with stearamide (C2) was delubricated inair at 530° C. All delubricated components were thereafter subjected toimpregnation according to the invention using an epoxy resin reinforcedwith CNT's.

The magnetic and mechanical properties were measured according toexample 1 and summarized in table 2 below.

TABLE 2 Resis- Core Overall Vaporization TRS tivity loss perfor- SampleTreatment [MPa] [μOhm*m] [W/kg] mance C 1. 350° C. Air 100 500 70 Poor(Stearamide) 2. 530° C. Air 50 200 50 Poor 3. 530° C. N₂ 120 150 55 GoodD 1. 350° C. N₂ 40 450 73 Poor (EBS Wax*) 2. 530° C. N₂ 120 120 58Accept- able E 1. 350° C. N₂ 40 400 76 Poor (Zn-Stearate) 2. 530° C. N₂90 100 73 Accept- able *Ethylene bis-stearamide (Acrawax ®)

As can be seen from table 3, the atmosphere and the temperature, atwhich the vaporization is conducted is of great importance.

Stearamide (sample C) is completely vaporized above 300° C. in bothinert gas atmosphere and in air. If the vaporization is performed in airat a too high temperature, the surface pores are blocked and prevents asubsequent impregnation to succeed giving low TRS (C2). If the heattreatment is conducted in an oxidative atmosphere at a lowertemperature, the impregnation can be successful, but gives unacceptablemagnetic properties (C1).

The EBS wax (sample D) cannot be vaporized at 350° C., but is removedfrom the compact at above 400° C. If the vaporization temperature is toolow, the residual organic lubricant will block the pores. Zn-stearate isvaporized at above 480° C., but leaves ZnO which leads to poorlyimpregnated compacts having low strength. The highest possiblevaporization temperature is preferred as this gives desired strainrelaxation and thus lowers coercivity and core loss.

Example 3

In this example, Somaloy®500 powder, available from Höganäs AB, having amean particle size smaller than the mean particle size of Somaloy®700was used. Somaloy®500 was mixed with 0.5 wt % of stearamide andcompacted at 800 MPa using a tool die temperature of 80° C. Two compactsamples was further subjected to a heat treatment in inert gas for 15minutes at 500° C. (sample F and G). Sample G was further subjected toimpregnation according to the invention using an anaerobic acrylic resinreinforced with CNTs.

The magnetic and mechanical properties were measured according toexample 1.

TABLE 3 Core Density TRS Resistivity loss Sample [g/cm3] [MPa] [μOhm*m][W/kg] F (Stearamide) 7.36 45 200 65 G (Stearamide) 7.36 130 200 65

Table 3 clearly shows that the invention can be used for manufacturingcomponents based on electrically insulated powders having finer particlesize.

Example 4

As starting material Somaloy®700, available from Höganäs AB, was used.All powder samples were mixed with 0.3 weight % of an organic lubricant,stearamide. The compositions were compacted at 1,100 MPa into TRS- bars(30×12×6 mm) of density 7.58 g/cm³. The die temperature was controlledto a temperature of 80° C. The mechanical properties were measuredaccording to example 1 and summarized in table 4 below.

After compaction the samples were subjected to a heat treatment in inertatmosphere for 15 minutes at 550° C. The porous network of the compactswere thereafter impregnated according to the invention using varioustypes of impregnants, i.e. reinforced curable polymers systems. Allliquid polymer composites show low viscosity at ambient temperature. Asreinforcement was SWNT used with 1.0% per weight of polymer.

TABLE 4 TRS TBS Polymer Rein- @RT @150° C. Sample resin Hardenerforcment [MPa] [MPa] H (Ref) None None None 40 40 I Epoxi type AmroyNone 70 50 polymer CA 25 CNT 130 110 (Amroy G4) J Epoxi type Isoforon-None 65 60 polymer diamine CNT 120 110 (TGDDM) K Acrylic-type AnaerobicNone 60 45 polymer CNT 120 105 (Omnifit 230M) L Thermoplatic None 70 65polymer None CNT 120 110 (PP)

As can been seen from Table 4, the TRS is improved significantly for alltypes, but when reinforced the improvement of mechanical strength (e.g.,TRS) is superior. By carefully choosing the polymer system (i.e.impregnant) the mechanical strength can be retained at temperatures of150° C. or higher.

Example 5

As starting material Somaloy®700, available from Höganäs AB, was used.All powder samples were mixed with 0.3 weight % of an organic lubricant,stearyl erucamide (SE). The compositions were compacted at 800 MPa or1,100 MPa using a die temperature of 60° C., to a density of 7.54 g/cm³,except for sample M3, which were compacted to 7.63 g/cm³ using 0.2 wt %SE.

After compaction the samples were subjected to a heat treatment in inertatmosphere at 550° C. for 15 minutes. The porous network of the compactswere thereafter filled using various types of impregnants, such ascurable polymers systems or non-curable oils, either reinforced or not.All impregnants show low viscosity at ambient temperature and are listedin Table 5.

The magnetic properties were measured on OD64×H20 mm cylinders aftermachining by turning into OD64/ID35×1−114,5 mm toroids (100 drive and 50sense).

TABLE 5 TRS Coer- Max. Rein- @ RT civity perme- Machin- Impregnantforcement [MPa] [A/m] ability ability M. Epoxy resin 1. None 70 180 500Acceptable 2. CNT 120 175 550 Excellent 3. CNT* 100 170 570 Good N.Acrylic resin 1. None 80 182 350 Acceptable (Loctite ® 290) 2. CNT 130178 450 Good O. Thermoplastic 1. None 60 184 450 Acceptable (LDPE) 2.CNT 120 180 550 Excellent P. Oil None 45 185 280 Poor (Nimbus ® 410) Q.Loctite None 65 180 360 Acceptable Resinol RTC R. Reference 1 — 120 225250 Very poor Steam treated** S. Reference 2 — 55 210 230 PoorConventional*** Pressed density 7.63 g/cm3 *Machined after steamtreatment **Green machined and subsequently heat treated in air at 530°C.

Low permeability can indicate presence of cracks and lamination, whichderives from abrasive forces and vibrations during the machining work.Also, the coercive force may be increased if the machining propertiesare reduced.

Signs of poor machining properties are smeared surface finish,break-outs, 10 cracks, and tool wear. Sample P to S are incorporated forcomparison.

Parts which have been green machined (S) and oxidized for improvedstrength (R), show not only high coercivity, but also poor machiningproperties and, thus, poor magnetic properties. Excellent magneticproperties 15 after machining can be obtained when the impregnator showgood machining properties together with high mechanical strength,especially samples M-2, N-2, and O-2.

1. A composite part comprising: a compacted powder composition; and apolymer composite comprising nanometer-sized and/or micrometer-sizedreinforcement structures, wherein the composite part has aninterpenetrating network between the compacted powder composition andthe polymer composite and wherein the reinforcement structures compriseone or more of: particles, platelets, fibers, whiskers, and tubes. 2.The composite part according to claim 1, wherein at least two dimensionsof the reinforcement structures are below 5 μm.
 3. The composite partaccording to claim 1, wherein the reinforcement structures comprisecarbon nanotubes.
 4. The composite part according to claim 1, whereinthe powder composition comprises a soft magnetic powder.
 5. Thecomposite part according to claim 3, wherein the powder compositioncomprises a soft magnetic powder.
 6. The composite part according toclaim 1, wherein the powder composition comprises an iron-based powder.7. The composite part according to claim 3, wherein the powdercomposition comprises an iron-based powder.
 8. The composite partaccording to claim 1, wherein the composite part shows a mechanicalstrength more than 100 MPa at above 150° C.
 9. The composite partaccording to claim 5, wherein the composite part shows a mechanicalstrength more than 100 MPa at above 150° C.
 10. The composite partaccording to claim 7, wherein the composite part shows a mechanicalstrength more than 100 MPa at above 150° C.
 11. The composite partaccording to claim 1, wherein the composite part has a density above 7.0g/cm³ and a TRS above 100 MPa at 150° C.
 12. The composite partaccording to claim 5, wherein the composite part has a density above 7.0g/cm³ and a TRS above 100 MPa at 150° C.
 13. The composite partaccording to claim 7, wherein the composite part has a density above 7.0g/cm³ and a TRS above 100 MPa at 150° C.
 14. A composite part producedaccording to a method for producing a composite part, the methodcomprising: compacting a soft magnetic powder composition comprising alubricant into a compacted body; heating the compacted body to atemperature above the vaporization temperature of the lubricant suchthat the lubricant substantially is removed from the compacted body;subjecting the obtained heat treated compacted body to a liquid polymercomposite comprising carbon nanotubes; and solidifying the heat treatedcompacted body comprising liquid polymer composite by drying and/or byat least one curing treatment, wherein the composite part has a densityabove 7.0 g/cm³ and a TRS above 100 MPa at 150° C.
 15. The compositepart according to claim 14, wherein the soft magnetic powder compositioncomprises an iron-based powder.